#include<bits/stdc++.h>
using namespace std;

int main(){
  char ch;
  cin>>ch;
  if(ch-'a'>=0&&ch-'a'<=25)cout<<"yes"<<endl;
  else if(ch-'A'>=0&&ch-'A'<=25)cout<<"yes"<<endl;
  else cout<<"no"<<endl;

  return 0;
}